Tailoring the Microstructure of Lamellar Ti₃C₂T_x MXene Aerogel by Compressive Straining

Abstract

Aerogels are attracting increasing interest due to their functional properties, such as lightweight and high porosity, which make them promising materials for energy storage and advanced composites. Compressive deformation allows the nano- and microstructure of lamellar freeze-cast aerogels to be tailored toward the aforementioned applications, where a 3D nanostructure of closely spaced, aligned sheets is desired. Quantitatively characterizing their microstructural evolution during compression is needed to allow optimization of manufacturing, understand in-service structural changes, and determine how aerogel structure relates to functional properties. Herein we have developed methods to quantitatively analyze lamellar aerogel domains, sheet spacing, and sheet orientation in 3D and to track their evolution as a function of increasing compression through synchrotron phase contrast X-ray microcomputed tomography (μCT). The as-cast domains are predominantly aligned with the freezing direction with random orientation in the orthogonal plane. Generally the sheets rotate toward flat and their spacing narrows progressively with increasing compression with negligible lateral strain (zero Poisson’s ratio). This is with the exception of sheets close to parallel with the loading direction ( Z ), which maintain their orientation and sheet spacing until ∼60% compression, beyond which they exhibit buckling. These data suggest that a single-domain, fully aligned as-cast aerogel is not necessary to produce a post-compression aligned lamellar structure and indicate how the spacing can be tailored as a function of compressive strain. The analysis methods presented herein are applicable to optimizing freeze-casting process and quantifying lamellar microdomain structures generally.

Cuttlefish-Bone-Structure-like Lamellar Porous Fiber-Based Ceramics with Enhanced Mechanical Performances

“…In fact, the wavelength (λ) of the product fabricated by the freeze-drying method, which is the average wall thickness plus its adjacent macropore size, follows an empirical power-law relationship with solidification velocity (ν) as shown in eq : λ = normalA × ν − n where n indicates the effect of freezing velocity on the wavelength (λ) and A refers to the attributions from the initial suspensions, such as viscosity. − Because AS02, AS12, AS22, AS32, and AS62 products are fabricated at the same freezing temperature and have the same solid loading, slurry viscosity as one potential crucial variable is investigated in this work.…”

Applications of X‐Ray‐Based Characterization in MXene Research

“…Reproduced with permission. [ 118 ] Copyright 2022, American Chemical Society. g) Subvolumes of the CT data of MXene aerogels at uncompressed and 50% of compression, showing sheet spacing reduction for initially 0° orientation, while sheet spacing reduction and rotation for initially 45° orientation and the buckling structure at initially 90° orientation.…”

“…This results in a substantial change in the microstructure, potentially closing and/or blocking the openings within the walls as the walls get closer (Figure 6e). [117] Rawson et al [118] classified the orientation of lamellar channels in MXene aerogels according to the polar angle of their sheet relative to the loading direction (Z) in 10°increments (Figure 6f). By an in situ micro-CT compression tests, they found that the predominant intradomain behavior is sheet reorientation toward the loading direction (Z) and simultaneous reduction in sheet spacing (Figure 6g).…”

Recent Advances in MXene‐Based Aerogels: Fabrication, Performance and Application

“…On account of inherent van der Waals forces between MXene layers, MXene nanosheets have an inevitable tendency to agglomerate and repacking, which leads to substantial difficulty in the formation of all‐MXene gels; therefore, it remains a major challenge in preparing aerogels solely composed of MXene and controlling their aerogel nano‐ and microstructure. [ 28 ] To address this key issue, a number of synthetic strategies have recently been reported, providing efficient solutions in the field. For example, Zhang et al developed a template‐free method for fabricating 3D macroporous MXene‐based aerogels through vacuum filtration and rapid freezing ( Figure a).…”